The components of high-temperature mechanical systems, such as, for example, gas-turbine engines, must operate in severe environments. For example, the combustor liners exposed to hot gases in commercial aeronautical engines typically experience coating surface temperatures of up to about 1150° C. to about 1400° C.
Typical components of high-temperature mechanical systems include a Ni or Co-based superalloy substrate. The substrate can be coated with a thermal barrier coating (TBC) to reduce surface temperatures. The thermal barrier coating may include a thermally insulative ceramic topcoat, and may be bonded to the substrate by an underlying metallic bond coat.
The component may be exposed to widely different temperatures during operation and when operation is ceased. These widely different temperatures may cause significant thermal stress to the TBC, which eventually may lead to spallation of the TBC from the substrate. The stress may be due to, for example, the substrate/bond coat and TBC having different coefficients of thermal expansion, or the substrate/bond coat and TBC experiencing different temperatures due to thermal gradients.